The problem I have has with pin holes in radiators is that if there is one pin hole there are many that are close to opening up. I end up playing a game of whack-a-mole. I fix one and then the pressure test reveals another. As a physicist I can't see how you can coat the inside of the radiator without losing efficiency unless it was a very special coating. I pulled the radiator out of my 53 3100 a couple of years ago and it's fine. I bought the truck in 1980 in SoCal and never put anything in it but water. I lived in the desert so it was a dry water.

Old enough to know better, too young to resist.